Although the legal drinking age in the United States is age 21, underage drinking is highly prevalent. Early onset of alcohol use is associated with increased risk of a number of subsequent adverse outcomes, including later heavy or problem drinking, likelihood of developing an alcohol use disorder, other substance involvement, and behavioral problems. Yet, there is a gap in our knowledge regarding what happens between first drink and the development of alcohol-related problems. Most research fails to characterize the very early course of alcohol involvement as it unfolds. The goal of the proposed study is to explore characteristics of the early drinking career including sequencing of, attainment of, and progression through what we term "drinking-related milestones." These include landmark events such as ever drinking, feeling high or drunk, regular drinking, binge drinking, and experience of alcohol-related problems of varying severity. The normative ordering of and progression through early drinking milestones will be described, with consideration of inter- and intra-individual variability. Because the importance of given risk factors and moderating influences may vary according to the stage of an individual's drinking trajectory, we will explain inter-individual differences in intra-individual change by determining the influence of individual (e.g., behavior regulation, expectancies, leisure activity) and contextual (e.g., family and peer influence, availability of alcohol) risk factors on onset and progression. Examination of these risk factors will be guided by an overarching theoretical model that draws on theories of substance use and health behavior. In addition, we will explore the extent to which both early initiation of alcohol use and a course characterized by rapid progression are associated with various outcomes such as academic achievement, substance use, and alcohol problems. To address these aims, 1,000 6th through 8th graders recruited from Rhode Island secondary schools will be assessed over a three-year period using a combination of relatively intensive (i.e., frequent) assessments of a narrow focus complemented by less frequent assessments that are broader in terms of content. The sample will be enriched by oversampling youth at risk for drinking. Specific aims will be addressed primarily using techniques of item response theory modeling, multilevel modeling, survival analysis, latent growth modeling, and latent transition analysis. When the specific aims are met, we will better be able to understand the prognostic significance of age of first drink and we will be able to isolate the unique influence of early drinking course on adverse outcomes. The proposed study will permit researchers to accurately pinpoint the stage at which an adolescent first exhibits risk for problematic drinking. The current application offers a more nuanced study that will finely map what happens between initiation and later use. Our findings will inform prevention efforts by identifying modifiable stage- specific risk factors for progression, maintenance, and regression (or desistence) of drinking during adolescence. Public Health Relevance: Early use of alcohol is associated with increased risk of a number of subsequent adverse outcomes, including heavy or problem drinking, likelihood of developing an alcohol use disorder, other substance involvement, and behavioral problems. It is only by understanding the early course of alcohol use that we can implement successful prevention strategies to reduce underage drinking and ultimately improve the mental and physical health of our population.